1. Field of the Invention
The present invention relates to a piezoelectric component and a method for manufacturing the piezoelectric component.
2. Discussion of Background
Piezoelectric components have been widely employed in various types of electronic devices such as filters, resonators or oscillators in the prior art. A basic requirement that must be fulfilled by a piezoelectric component is that, since desired characteristics are achieved by utilizing the resonance characteristics, the degree of accuracy of its resonance frequency be high.
The following three methods are well known as means for achieving desired resonance characteristics by adjusting the resonance frequency of a piezoelectric component. In the first method, the thickness of the piezoelectric substrate is adjusted through polishing. In the second method, the thickness of the electrode is adjusted and in the third method, the desired resonance characteristics are achieved through the adjustment of the quantity of resin deposited onto the resonating part.
However, the first method poses problems in that it is difficult to perform polishing at the accuracy required for adjusting the resonance frequency and in that inconsistency occurs in the resonance frequency. The second method requires a great length of time and a great deal of work and, furthermore, it does not achieve good reproducibility. The third method presents a problem in that it is difficult to finely adjust the quantity of resin to be deposited onto the resonating part.
An improvement on the third method is disclosed in, for instance, Japanese Unexamined Patent Publication No. 160121/1981. This publication discloses a method whereby the resonance frequency of a piezoelectric substrate to which a mass substance is added in advance is measured, a correct quantity of the mass substance is removed by radiating a laser beam which is controlled in correspondence to the degree of deviation of the resonance frequency relative to the frequency setting on the mass substance added to the piezoelectric substrate to adjust the resonance frequency to the frequency setting.
However, the publication does not refer to specifically how the mass substance should be processed or what type of laser beam should be employed. Consequently, the method disclosed in the publication above is not sufficient to provide a piezoelectric component with a high degree of accuracy in the resonance frequency and a high Q value for its resonance characteristics.
It is an object of the present invention to provide a piezoelectric component having a resonance frequency which is adjusted with a high degree of accuracy.
It is a further object of the present invention to provide a piezoelectric component with a high degree of accuracy in its resonance frequency and a high Q value for its resonance characteristics.
It is a still further object of the present invention to provide a method for manufacturing piezoelectric components in large quantities that are free of inconsistency in their characteristics through simple processes.
In order to achieve the objects described above, the piezoelectric component according to the present invention includes a piezoelectric substrate and a deposit. The piezoelectric substrate is provided with at least one resonating part. The deposit is added onto a surface of the resonating part and is provided with a plurality of indented portions within a surface enclosed by outer edges.
Since the deposit is added onto the surface of the resonating part, as described above, a load corresponding to the mass of the deposit is applied to the resonating part to set the resonance frequency of the resonating part at a value that corresponds to the mass of the deposit and the load.
Since the deposit is provided with a plurality of indented portions within its surface enclosed by the outer edges, the resonance frequency is set at a value with a high degree of accuracy that corresponds to the number of indented portions, the volume of the indented portions, the distance between the individual indented portions, the pattern of the indented portions and the like.
The indented portions are formed so that the load applied by the deposit to the resonating part is evenly distributed at the surface of the resonating part. Evenly distributing the load in this manner contributes to achieving a higher accuracy in the resonance frequency.
In the method for manufacturing a piezoelectric component according to the present invention, during the step for adjusting the resonance frequency of the piezoelectric component, a laser beam whose wavelength is within a range of 350 to 2000 nm is radiated onto a surface of the deposit and the deposit is trimmed through being irradiated by the laser beam to form indented portions. Thus, the mass of the deposit is reduced in correspondence to the number of indented portions, the size of the indented portions, the distance between the individual indented portions, the pattern of the indented portions and the like to adjust the load applied by the deposit to the resonating part.
Since the indented portions are formed through radiation of a laser beam, their quantity, size, pattern and the like can be set with a high degree of accuracy. As a result, the resonance frequency can be set at a value with a high degree of accuracy.
For the formation of the indented portions, a laser beam having a wavelength within the range of 350 to 2000 nm is radiated. By using a laser beam having a wavelength within this range, indented portions can be formed at the deposit without resulting in any degradation in the piezoelectric characteristics.
It is desirable that the deposit be constituted of resin. By constituting the deposit of resin, the required indented portions can be formed with ease through radiation of a laser beam. It is particularly desirable to use a resin containing a carbon filler at 0.1 to 20 wt %. Since the degree to which a laser beam is absorbed by resin can be adjusted in correspondence to the carbon filler content, the intensity of the required laser beam can be indirectly adjusted by using a resin containing a carbon filler at 0.1 to 20 wt %.
A suitable laser to be employed is a solid-state YAG laser. In particular, the fundamental harmonic (wavelength; 1.06 xcexcm), the second harmonic (wavelength; 530 nm) or the third harmonic (wavelength; 353 nm) of a solid-state YAG laser is ideal.
Furthermore, the present invention discloses a technology for adjusting the resonance frequency without lowering the Q value of a piezoelectric component with an even higher degree of accuracy. This technology may be adopted in an ideal manner when adjusting the resonance characteristics of an oscillator, a resonator or the like that requires highly accurate adjustment of the resonance characteristics.
In the piezoelectric component according to the present invention, the surface of the deposit is scored with indentations and projections, and when the surface roughness of the indented and projected surface is assigned Rmax and the resonance wavelength of the resonating part is assigned xcex0, a relationship expressed as Rmax/xcex0xe2x89xa60.008 is satisfied.
With the surface of the deposit constituted of indentations and projections, the mass of the deposit can be finely controlled in correspondence to the state of the indentations and projections at the surface of the deposit to achieve fine and highly accurate adjustment of the resonance frequency.
The Q value of the resonance characteristics is greatly affected by the state of the indentations and projections at the surface of the deposit. When standardized surface roughness R0 is defined as (Rmax/xcex0) with Rmax being the surface roughness of the indented and projected surface and ;Lo being the resonance wavelength of the piezoelectric component, in the range over which the standardized surface roughness R0 is at 0.008 or less, an almost constant high Q value can be achieved regardless of any fluctuation in the standardized surface roughness R0. In the range over which the standardized surface roughness R0 is at 0.008 or more, the Q value is reduced almost exponentially as the standardized surface roughness R0 increases.
In order to obtain a piezoelectric component with the surface of its deposit constituted of indentations and projections, a laser beam having a wavelength of 350 nm or less is irradiated on the deposit to trim the surface of the deposit.
With a laser beam having a wavelength of 350 nm or less, the surface of the deposit can be trimmed evenly to achieve a standardized surface roughness R0 of 0.005 or less, which makes it possible to achieve high accuracy in the resonance frequency and a high Q value. It has been confirmed that when trimming is performed using a laser beam having a wavelength longer than 350 nm, e.g., a laser beam having a wavelength of 353 nm, the Q value becomes lower.
It is desirable to measure the resonance frequency of the piezoelectric component and radiate a laser beam controlled in correspondence to the degree of deviation of the measured resonance frequency relative to the target resonance frequency on the deposit during the trimming process. Through this adjustment method, the resonance frequency can be adjusted to the target resonance frequency with ease.
By repeating the adjustment described above, the accuracy of the resonance frequency adjustment can be improved. During this process, if the wavelength of the laser beam radiated on the deposit is 350 nm or less, only an extremely small quantity of the laser beam is converted to heat. Thus, even immediately after radiation of the laser beam, the resonance frequency of the piezoelectric component can be measured. Consequently, the trimming adjustment process employing the laser beam can be repeated without allowing intervals.
The laser beam employed for the trimming may be set in either the single-mode or the multi-mode. Since the intensity of the laser beam is distributed evenly within the spot when set in multi-mode, trimming can be performed more consistently through radiation of laser beam in the multi-mode to achieve a piezoelectric component with a high degree of accuracy in its resonance frequency and a high Q value for its resonance characteristics.
Alternatively, trimming may be achieved by scanning the laser beam spot over the entire surface of the deposit evenly. In this case, the quantity of shift in the resonance frequency per scan is constant. As a result, by selecting the number of scans to be performed with the laser beam spot, the resonance frequency can be adjusted.
In addition, to irradiate the deposit, a pulse oscillation type laser system may be employed to radiate a pulse laser beam over the entire surface of the deposit evenly.
As described above, the quantity of shift in the resonance frequency per laser beam irradiation is constant. Consequently, the resonance frequency can be adjusted in correspondence to the number of times that the pulse laser beam is radiated.